The advantages of the present invention can be described best by showing the discrepancies between the ideal and the car transmissions currently available.
The Ideal Transmission
Theoretically the ideal car transmission transmits the engine power to the wheels so that for any required power level, the engine works at its highest efficiency point, whatever the car speed.
An engine works at its highest efficiency when the throttle is pushed deeply, as is shown in the graph of FIG. 10 showing the specific fuel consumption of a diesel engine. The power is modulated rather by changing the engine speed than by changing throttle. For example, driving on a highway at 120 km/h at constant speed requires only about 25 HP. The optimum engine speed is then about 1300 RPM for modern engines. The required transmission torque ratio is then 0.441, while a typical ratio of an actual gearbox varies from 0.90 to 0.65 in highest ratio. Conclusion is that the ratios of the current gearboxes are not high enough for optimum engine efficiency.
FIG. 10 illustrates the statement above. With the known gearboxes, the car drives at 120 km/h at 2400 RPM and with 73 Nm from the engine. The specific fuel consumption (SFC) is then 265 g/kWh. In the ideal case (of a low torque engine) the engine speed must be reduced only to 1700 RPM to obtain the highest efficiency. The engine produces then 103 Nm with a SFC of 225 g/kWh. This is a fuel saving of 15%. This is for example a fuel saving from 6.5 l/100 km to 5.5 l/100 km, only obtained from improving the engine operating point, not considering the efficiency of the transmission.
For drive away the ideal transmission needs an infinite torque ratio.
When the car is still at zero speed and the engine speed is at least idle speed, the transmission ratio must be infinite. Current solutions with a slipping clutch or a slipping torque converter spoil a lot of energy during every launch.
The above must remain true also during and after a sudden throttle position change. (A throttle position change is in fact a change in requested engine power.)
This means that the ratio should be able to change very fast. Suppose the car drives at a constant moderate speed with 85% throttle for optimal consumption. The engine produces only a small fraction of the available engine power. If acceleration is requested, without ratio change, the engine can only accelerate with the remaining 15% throttle, so that the low power can only increase with 15%. Thus immediate downshifting is needed to obtain the requested engine power: the transmission must change immediately the ratio so that the engine accelerates to the engine speed where it produces the requested power with optimal efficiency.
The ideal transmission must be environmental friendly, should not contain non-recyclable or toxic materials or oils.
The ideal efficiency should be 100%, size, weight and cost as low as possible, with perfect reliability and durability.
Limitations of Actual Car Transmissions
    MT=Manual Transmission with dry clutch    AT=Automatic transmission with torque converter, possibly equipped with lock-up    DCT=Double Clutch with wet or dry clutches    CVT-belt=Continuously Variable Transmission with a belt between 2 conical pulleys    CVT-toroid=Continuously Variable Transmission with half or full toroidal pulleys    HSD=Hydrostatic drive. This is a hydraulic system with a variable axial piston pump, driven by the engine and a variable hydraulic motor driving a gearbox or directly the wheels. The output speed is variable from zero to a certain speed and by switching a valve, the rotation sense can be reversed.
Efficiency(highway)ProblemsMThighMuch more gears and a larger spread are needed to improve fuelefficiencyeconomy (1)ca 88-97%More gears require too much shifting and confuse the driverATmoderateMuch more gears and a larger spread are needed to improve fuelefficiencyeconomy (1)ca 88-92%More gears result in higher costDuring shifting the efficiency is low. More shifting counteracts theimprovement of fuel consumption.DCThighMuch more gears and a larger spread are needed to improve fuelefficiencyeconomy (1)89-95%More gears result in higher costMore gears -> more shifting-> more use of the clutch-> moreenergy dissipationCVT-lowThe belt should not slip to transmit torque, but the belt must slipbeltefficiencyto change ratio. So low efficiency when changing the ratio or slow<85%?ratio changes.High pressure is needed in the pulley, which leads to highhydraulic losses.CVT-lowThe pulleys are rolling over each other with a drilling motion. Thistoroidefficiencydrilling motion creates a forced macroslip. This slip reduces the<85%?efficiency and creates heat which needs to be dissipated.HSDVery lowHeavy system, often used for off-highway (wheel loaders...) orefficiencysmall trucks. Without gearbox, low max speed ratio in anCa 70-80%acceptable efficiency range.
(1) Refers to the history of the typical number of gear ratios in a passenger car:
MTATDCTHighest gear ratioyears 70 and43 (+1st gear used1earlieronly in kickdown)years 80 9054about 0.90 to0.95years 2000 20075-65-6-76-7about 0.65 to0.90Conclusion:
MT, AT, DCT: although always more gears are needed to improve fuel consumption, there is somewhere a practical limit where no further improvement is possible. The highest ratios are still not high enough for optimum fuel economy.
CVT: low efficiency; also the highest ratio is still not high enough for optimum fuel economy.
There is therefore a need for an improved gearbox or transmission that overcomes the above indicated limitations and disadvantages.